1. Field of the Invention
The present invention relates to a gas turbine moving blade wherein there is formed, within a blade profile portion, a cooling passage for the flow of a cooling medium in a plurality of rows in a blade chord direction on a blade leading edge side and on a blade trailing edge side, respectively. Also formed within a blade root portion are a supply side passage connected to the respective cooling passage for supplying the cooling medium to the cooling passage and a discharge side passage connected to the respective cooling passage for discharging the cooling medium after used for cooling, so that the moving blade is cooled from its interior.
2. Description of the Prior Art
In a recent gas turbine moving blade using a high temperature operating gas of which a turbine inlet temperature is elevated, there is provided within a blade profile portion a cooling air passage in a plurality of rows in a blade chord direction for flow of a low temperature compressed air to cool the moving blade from its interior. Thus, a temperature of the moving blade exposed to the high temperature operating gas is lowered to or below an allowable value which is lower than a moving blade metal temperature and may maintain the structural strength.
In such air cooling of the moving blade, cooling air supplied into the moving blade passes through an inner cooling passage to provide convention cooling of the moving blade from its interior. The cooling air is then discharged into the high temperature operating gas flowing on an outer periphery of the moving blade through holes provided at a leading edge portion, a blade tip portion and a trailing edge portion of the moving blade, of which temperature is liable to be elevated due to the respective shape of structure, to provide film cooling of the edge or tip portions.
FIG. 4, is a longitudinal cross sectional view of a blade a thickness central portion of a prior art gas turbine moving blade. Cooling air passing through a moving blade interior provides cooling of the moving blade.
As shown in FIG. 4 in an interior of a blade profile portion 04 of a moving blade 01, there is provided a cooling passage 05 in a blade lengthwise direction between a blade root portion 02 and a blade tip portion 03. The cooling passage 05 is provided in a plurality of rows in a blade chord direction, which is a front and rear direction, of the moving blade 01 and is sectioned into a plurality of systems in the blade chord direction.
Cooling air 06 is introduced into the cooling passage 05 from an air passage provided within a rotor (not shown). The air flows to an outer periphery of the rotor of which the blade root portion 02 is fitted so as to be rotated together with the moving blade 01, via a supply side passage 010 provided within the blade root portion 02 and, while passing through within the moving blade 01 in the lengthwise direction between the blade root portion 02 and the blade tip portion 03, providing convection cooling of the moving blade 01 from its interior.
A portion of the cooling air 06 entering the supply side passage 010, after providing convection cooling of the moving blade 01, is discharged with a high velocity into a high temperature operating gas 013. The cooling air flows on an outer periphery of the moving blade 01, through openings 07 etc. provided at a leading edge portion 011 of the moving blade 01 so as to provide film cooling of a blade profile portion 04. Also, a portion of the cooling air 06, after providing convection cooling of a blade trailing edge portion 012, is discharged into the high temperature operating gas 013 through holes 08 provided at the blade trailing edge portion 012 and openings 09 provided at the blade tip portion 03.
Incidentally, in FIG. 4, numeral 014 designates a turbulator, which is disposed, transverse to a flow of the cooling air 06, within the cooling passage 05 for making the flow of the cooling air 06 turbulent so as to enhance the cooling efficiency.
As mentioned above, in the prior art gas turbine blade, there are employed various cooling structures so that a cooling is strengthened, a high temperature at a portion, where a blade thickness is made small for an operating efficiency of the moving blade 01. Therefore, where structural strength is small and a high temperature strength becomes severe, a structural strength is maintained and a lowering of efficiency is prevented.
Further, in a recent trend toward a high temperature gas turbine, use of higher temperature gas as an operating gas is contemplated for further improvement of a gas turbine thermal efficiency and, for this purpose, there are attempts to use a material which is excellent with respect to high temperature strength for the moving blade 01 as well as of further strengthening a cooling of the moving blade 01.
If compressed air is used as the cooling medium, as mentioned above, a sufficient cooling effect cannot be obtained due to the small thermal capacity. Hence, it is necessary to use steam as the cooling medium. Steam has a high thermal capacity and is able to enhance the cooling efficiency.
In a steam cooled blade in which cooling is effected by steam flowing within the moving blade 01, if the steam, after being used for cooling, is discharged into the high temperature operating gas 013, likewise the cooling air 06 mentioned above, the thermal efficiency of the gas turbine is lowered greatly. Thus, it is necessary that all the steam used for cooling is recovered from the interior of the moving blade 01 so that the thermal energy of the recovered steam can be recovered again by a steam turbine.
In other words, if a cooling method in which steam is discharged into a high temperature operating gas 013, likewise the cooling air 06, there occur problems such as temperature lowering of the high temperature operating gas 013 which is largely due to the steam discharge an internal efficiency of the turbine is substantially reduced. Also, there is no contribution of thermal energy recovered from the cooling of the moving blade 01 in an improvement of thermal efficiency of a gas turbine plant. Thus, an aimed improvement of thermal efficiency of the gas turbine is hindered.
Accordingly, if steam is used for cooling of the moving blade 01, there is a necessity of providing a discharge side passage within the blade root portion 02 for discharging the steam, after being used for cooling, from the cooling passage. While the following two points remain the same as in the above-mentioned air cooling, that is, a supply side passage is to be provided at the blade root portion 02 for supplying a flow rate of steam, which is necessary for cooling of the moving blade 01, into the cooling passage 05 and a supply side passage is to be provided both on the leading edge portion 011 side and the trailing edge portion 012 side of the blade for supplying a low temperature steam to the vicinity of the leading edge portion 011 and the trailing edge portion 012 where the high temperature strength becomes severe.
That is, a supply side passage is to be provided within the blade root portion 02 in the vicinity of the leading edge portion 011 and the trailing edge portion 012, respectively, of the moving blade 01 for supplying a low temperature steam into the respective cooling passage of the leading edge portion 011 and the trailing edge portion 012. Also, a discharge side passage is to be provided between the respective supply side passage within the blade root portion 02 for discharging the steam from the cooling passage in the vicinity of the central portion of the moving blade 01 for recovery of the steam after being used for cooling and having an elevated temperature.
Therefore, it becomes necessary to provide two systems of the supply side passage, having an increased passage area due to replacement of the cooling medium from air to steam and to provide at least one system of the discharge side passage to be disposed between the supply side passages. The systems are provided within the blade root portion 02 which has a small volume capacity, and there occurs a problem that arrangement of these passages becomes difficult.